The present invention relates to an image processing apparatus, an image processing method, an imaging apparatus, an information storage medium, and the like.
An imaging apparatus such as an endoscope is desired to generate a deep-focus image in order to facilitate diagnosis performed by a doctor. In order to satisfy such a demand, the depth of field of an endoscope is increased by utilizing an optical system having a relatively large F-number.
In recent years, an imaging element having about several hundred thousand pixels has been used for endoscope systems. The depth of field of the imaging element is determined by the size of the permissible circle of confusion. Since an imaging element having a large number of pixels has a small pixel pitch and a small permissible circle of confusion, the depth of field of the imaging apparatus decreases. In this case, the depth of field may be maintained by reducing the aperture of the optical system, and increasing the F-number of the optical system. According to this method, however, the optical system darkens, and noise increases, so that the image quality deteriorates. Moreover, the effect of diffraction increases as the F-number increases, so that the imaging performance deteriorates. Accordingly, a high-resolution image cannot be obtained even if the number of pixels of the imaging element is increased.
The depth of field may be increased by acquiring a plurality of images that differ in in-focus object plane, and generating a synthetic image by synthesizing only in-focus areas (see JP-A-2000-276121). The depth of field may also be increased by increasing axial chromatic aberration using an optical system, acquiring a plurality of images that differ in in-focus object plane depending on the channel, and processing the resulting images (see JP-T-2008-532449). The depth of field can be increased while maintaining high resolving power by applying such technology to an endoscope system.